Synthese von (−)-(R)-Nephthenol und (−)-(R)-Cembren A

Synthesis of (?)-(R)-Nephthenol and (?)-(R)-Cembren A Starting for L -serine,(?)-(R)-nephthenol((?)- 2 ) and (?)-(R)-cembren A((?)- 3 ) were synthesized.     

Synthesis of enantiomerically pure (S)-(−)-propranolol from sorbitol

Synthesis of enantiomerically pure (S)-(−)-propranolol, the most active optical isomer of the widely used β-Sympatholyticum, was achieved in high optical yield starting from sorbitol, an inexpensive and easily accessible carbohydrate. Via regioselective protection and coupling of -naphthol, the key intermediate 5 was obtained. Deprotection of the intermediate acetals and successive oxidative degradation followed by some simple conversion steps lead to the formation of (S)-(−)-propranolol with high optically purity.     

Enantioselective syntheses of (−)-anisomycin and its propionate derivative (3097-B1)

Facile syntheses of (−)-anisomycin and 3097-B1 from divinylcarbinol 3 in an overall yield of 12.2% and 13.2%, respectively are described.     

Negative-ion-negative-ion neutralization-reionization (−NR−)

There are four neutralization-reionization processes which can be studied. In the first two, gaseous cations are collisionally reduced and the resulting fast neutrals are either oxidized by collisional electron removal (NR) or reduced further by collisional electron attachment (NR^?). In the third and fourth processes, gaseous anions are collisionally oxidized and the resulting fast neutrals are either oxidized further by collisional electron removal (^?NR) or reduced by collisional electron attachment (^?NR^?). These four processes are illustrated briefly using the interrelated species [SF₅]⁺ and [SF₅]^?. Negative-ion-negative-ion neutralization-reionization (^?NR^?) processes are illustrated for [CH₃O]^?, [C₂H₅O]^?, [CO₃]^? and [HCO₃]^? and compared with ^?NR processes. In addition, collisional electron attachment ionization of fast neutrals formed in unimolecular fragmentation of cations is illustrated. The ^?NR^? studies of [CO₃]^? and [HCO₃]^? show that both CO₃ and HCO₃ are stable neutral species with lifetimes greater than 0.7 μs.     

Optically active (−)-5,6-dicarba-nido-decaborane (12)

One-way conversion of the racemic (±)-5,6-dicarba-nido-decaborane (12) to its laevorotatory enantiomer by (+)-N-methylcamphidine is reported.     

Stereocontrolled Synthesis of (−)-5,11-Dideoxytetrodotoxin

New derivatives of an intriguing marine natural product are now accessible. The first asymmetric synthesis of the simple tetrodotoxin analogue, 5,11-dideoxytetrodotoxin ( 3 ), was achieved. Hydroxylation at position C8 of the key intermediate 1 relied on the neighboring trichloroacetamide group, and stereoselective elaboration of the vinyl group gave α-hydroxylactone 2 , which was transformed into the title compound through a new guanidylation method.     

Total Synthesis of (−)-(2R)-Dihydromyricoidine

An asymmetric synthesis of the spermidine alkaloid (?)-(2R)-dihydromyricoidine ( 5 ) was performed by employing two ring-enlargement reactions. The chiral center was introduced by a diastereoselective Michael addition of perhydropyridazine ( 7 ) to the α,β-unsaturated ester 6 . The (Z)-C?C bond was obtained by a selective Wittig reaction. The synthetic compound 5 was found to have a negative value for the specific rotation. This is in contrast to that of the natural product reported in the literature. Therefore, as an outcome of this synthesis, the absolute configuration of the natural alkaloid should be inverted to be as shown in structure V .     

Über Cs2TlBr5 – ein Pentabromothallat (III) mit tetraedrischen TlBr4− - und oktaedrischen TlBr63− -Anionen

On Cs₂TlBr₅ — a Pentabromothallat (III) with Tetrahedral TlBr₄^? and Octahedral TlBr₆^3? Anions Cs₂TlBr₅ has been synthesized by crystallization from aqueous TlBr₃/CsBr solutions. The orthorhombic structure (a = 1330.2(11); b = 777.0(3); c = 2349.3(6) pm; Z = 8, space group Pnma-Nr. 62) contains isolated tetrahedral TlBr₄- and octahedral TlBr₆^3? anions which are packed together with the Cs⁺ cations in an anti-CaWO₄ arrangement. At 260°C Cs₂TlBr₅ decomposes irreversibly to Cs₃Tl₂Br₉ and CsBr.     

Die Reaktion von Tellurhexafluorid mit Trimethylamin,Strukturen der TeF5−- und SeF5−-Anionen

Reaction of Telluriumhexafluoride and Trimethylamine, Structures of the TeF₅^? and SeF₅^? Anions The reaction of TeF₆ and (CH₃)₃N is of the redox kind, resulting in reduction of tellurium: X-ray single crystal analysis reveals the compounds (CH₃)₂N? CH₂? N(CH₃)₂⁺TeF₅^? and [(CH₃)₃NH⁺]₅(TeF₅^?)₃(HF₂^?)₂. By comparison with published data it can be shown that this mixture is identical to previously published [(CH₃)₃N]₂TeF₆. The latter was supposed to be one of the few examples of tellurium in a coordination state of eight. (CH₃)₄N⁺TeF₅^? and (CH₃)₄N⁴SeF₅^? are obtained and their structure is investigated by single crystal x-ray methods also. The anions SF₅^?, SeF₅^? and TeF₅^? are discussed in terms of weak interactions.     

A convenient stereoselective synthesis of (R)-(−)-denopamine and (R)-(−)-salmeterol

β-Adrenoreceptor agonists (R)-(−)-denopamine (R)-1 and (R)-(−)-salmeterol (R)-2 have been prepared in good overall yield and high enantioselectivity through a biotransformative pathway.